H FLORA OF TASMANIA. 
these the most important are Brown's ' Prodromus,' of which the only published volume appeared in 
1810; the 'Plantge Preissianae/ edited by Professor Lehmann, and containing descriptions, by vari- 
ous authors, of about 2250 species (including Cryptogamise) of Swan River plants; Dr. Mueller's 
various Reports on the Flora of Victoria, and his numerous papers on the vegetable productions of 
that colony ; and Lindley's Appendices to Mitchell's Travels. 
The unpublished materials chiefly consist of the vast collections of Australian plants made 
during the last half-century, and these having been obtained from all parts of the continent, and care- 
fully ticketed as to locality, etc., supply abundant materials for the investigation of the main features 
of the Australian Flora. In another part of this Essay I propose to give a short summary of the 
labours of the individuals by whom these and other Australian collections have been principally ob- 
tained, and of the routes followed by the expeditions which they accompanied. 
The majority of the collections were, either wholly or in part, transmitted to Sir William 
Hooker, forming the largest Australian herbarium in existence, and of which the published portion 
is in value greatly exceeded by the unpublished ; for although about two-thirds of the plants have 
been described, only about half of these have been brought together in a systematic form ; nor, since 
the publication of Brown's Appendix to Flinders' Voyage, has the Flora of the whole continent been 
considered from a general point of view. And, before entering on the field of inquiry so successfully 
explored by Brown half a century ago, I must pay my tribute to the sagacity and research exhibited 
in the essay to which I have alluded. At the time of its publication, not half the plants now de- 
scribed were discovered, vast areas were yet unexplored, and far too little was known of the vegetation 
of the neighbouring islands to admit of the Australian Flora being studied in its relation to that of 
other countries. Nevertheless we are indebted to Brown's powers of generalization for a plan of the 
entire Flora, constructed out of fragmentary collections from its different districts, which requires but 
little correction from our increased knowledge, though necessarily very considerable amplification. 
Although he could not show the extent and exact nature of its affinities, he could predict many of 
them, and by his detection of the representatives of plants of other countries under the masks of 
structural peculiarity which disguise them in Australia, he long ago gave us the key to the solution 
of some of those great problems of distribution and variation, which were then hardly propounded, 
but which are now prominent branches of inquiry with every philosophical naturalist. 
In the Introductory Essay to the New Zealand Flora, I advanced certain general propositions 
as to the origin of species, which I refrained from endorsing as articles of my own creed : amongst 
others was the still prevalent doctrine that these are, in the ordinary acceptation of the term, created 
as such, and are immutable. In the present Essay I shall advance the opposite hypothesis, that spe- 
cies are derivative and mutable; and this chiefly because, whatever opinions a naturalist may have 
adopted with regard to the origin and variation of species, every candid mind must admit that the 
facts and arguments upon which he has grounded his convictions require revision since the recent 
publication by the Linnean Society of the ingenious and original reasonings and theories of Mr Dar- 
win and Mr. Wallace. 
Further, there must be many who, like myself, having hitherto refrained from expressing any 
positive opinion, now, after a careful consideration of these naturalists' theories, find the aspect of the 
question materially changed, and themselves freer to adopt such a theory as may best harmonize 
with the facts adduced by their own experience. 
The Natural History of Australia seemed to me to be especially suited to test such a theory, 
on account of the comparative uniformity of its physical features being accompanied with a great 
